Prior to the present invention, it has been known to make isophorone through the aldol condensation of acetone. However, the nuances, variations, and complications of this seemingly simple reaction may be tentatively appreciated by noting the summary of a paper by Salvapati, Ramanamurty, and Janardanarao (Journal of Molecular Catalysis, 54 [1989] 9-30): "Catalytic self-condensation of acetone is a very complex reaction and numerous products are possible via competitive self-condensation and cross-condensation between the same or different ketones that are formed in the reaction. All the major products of the reaction, diacetone alcohol, mesityloxide, phorone, mesitylene, isophorone, 3,5-xylenol and 2,3,5-trimethylphenol find important industrial applications. The reaction is catalysed by acids as well as bases, and it can be carried out in both liquid and vapour phases. The selectivity of the reaction for the desired product is achieved by proper choice of catalyst and experimental conditions. This paper reviews the recent developments in the process of self-condensation of acetone, evaluating the significance of various parameters for obtaining the desired product." The Salvapati et al article goes on to describe in some detail and with copious structural formulas the various possibilities in the autocondensation of acetone and the aromatization of isophorone, especially in the presence of acetone. It is clear that the catalyst and conditions for the aldol condensation of acetone must be carefully chosen to achieve a practical selectivity for isophorone.
This invention is designed to employ effectively a catalyst of the type described by Schutz in U.S. Pat. No. 4,970,191; preferably the catalyst is enhanced by the process of extruding or otherwise forming it described by Schutz and Cullo in U.S. Pat. No. 5,153,156. Methods of making isophorone described by Schutz in U.S. Pat. No. 5,055,620 and by Schutz and Cullo in U.S. Pat. No. 5,202,496 are also especially applicable to the present invention; use of the catalyst to react acetone in the vapor phase is particularly of interest in the present invention. The Schutz and Schutz/Cullo patents employ pseudoboehmite reacted with an acid to form a gel, to which is added magnesium oxide or hydroxide in particular ratios, followed by agitation, heating, and calcining. These patents are incorporated herein by reference in their entirety.
However, our invention may use also, or in place of the catalysts of the above-recited Schutz and Schutz/Cullo patents, a catalyst of the type disclosed by Reichle in U.S. Pat. No. 4,165,339 and 4,458,026 and/or Papa et al U.S. Pat. No. 4,535,187, to the extent they are practical. As mentioned below, this invention is a process for the vapor phase aldol condensation of acetone to make isophorone, and is intended to include the use of any catalyst which will catalyze such a reaction, including catalysts described in any of the above-cited patents which are known to do so, to the extent applicable.